瑜伽論記 4.293

4.293

言設復於此內外空性不證會者等者，明初學者於內外空不能證會便應思惟無常苦想，不為我及慢所動，便於內外二空俱證。基云：此即顯空無我行名為空行，空無有情及法我故。

The statement "if furthermore they do not realize and accord with this internal and external emptiness, etc." clarifies that when initial learners cannot realize and accord with internal and external emptiness, they should reflect on the perceptions of impermanence and suffering so as not to be moved by self and conceit, and then they will realize both internal and external emptiness. Kuiji says: this reveals that the practice of emptiness and non-self is called the practice of emptiness, because it is empty of a self of sentient beings and a self of dharmas.